The objective of this project is to investigate the immunogenetic properties of alloantigen systems of the mouse. The recombinational analysis of the H-2 gene complex and the preparation of H-2 congenic lines bearing new recombinant haplotypes is a major component of the project. The new recombinant haplotypes are used to produce more highly specific serological reagents. Studies will be carried out to further define the genetic basis of immunological responsiveness.